IT professionals see Solid State Disk (SSD) products as a means to obtain higher performance and better response
times. Having higher IOPS and shorter latencies than HDD, SSDs are being deployed in external storage arrays in
conjunction with, or replacing HDDs. While high IOPS is frequently the metric for assessing drive and array
performance, in many cases latency is equally as important. For example, in an OLTP application, short response
times are critical. A transaction may require many successive queries to a database, where each query depends on
answers returned from the previous query. User response times are entirely dependent on how quickly storage
can return answers to the queries.

While SSDs can enable short response times, the connection to the storage array may limit these responses.
An increasing number of current generation storage systems are providing multiple types of host interfaces
for the same storage system, giving customers a wide variety of choices for connectivity to these storage
systems. Block host interfaces, including Fibre Channel, iSCSI and SAS are all becoming increasingly
available for today’s storage systems.

LSI commissioned Demartek to compare four block interface and speed combinations on the same NetApp E2600
storage system for basic performance. These four host interfaces were:

8Gb Fibre Channel (FC)

10Gb iSCSI

1Gb iSCSI

6Gb SAS

At first glance, one might assume that the interfaces with the highest line rates would provide the best
overall performance, but we found that this was not the case.

We found that the best overall performance for this storage system was with the 6Gb SAS host connection,
followed very closely by the 8Gb Fibre Channel host connection. This is due to the low latency
characteristics for 6Gb SAS connections, as measured from the application host server. Although 6Gb SAS
has a lower line rate than 8Gb Fibre Channel or 10Gb iSCSI connections, its overall protocol overhead is
lower than the other interfaces tested, and makes an excellent choice as a host interface for storage systems.

More information

To be notified when we post new deployment guides, evaluation reports and commentaries, sign-up for our free monthly newsletter,
Demartek Lab Notes.
We do not give out, rent or sell our email list.